I tried using another cable that I know works for sure. Same problem as the post above. What's even weirder is that the drive works fine with just the main line plugged into the one port. Plugging in the other half of the Y-cable makes no difference.

Any ideas? Is the drive safe to use/access with this sort of behaviour? I don't want to risk data corruption.

The external is a Toshiba 160GB 5400rpm SATA HDD. I'm not sure of the exact model. The enclosure is a Vantec Nexstar TX. All 4 partitions (NTFS or otherwise) are reported as "Healthy" (including the "Active" Vista partition).

From what you've posted so far, I'll assume you got the drive access problem taken care of but now are unable to access a lot of the files due to lack of permissions.

If, for example, you've removed that drive from another PC and installed it in the external enclosure for the purpose of copying the files; then most of the files on that drive would have their permissions tied to the SID of the User/s of the PC it came out of, and not to your User SID on the machine that drive is now connected to. Meaning; you only have read permission on many of the files and no access at all to many others.

The solution is to first take ownership at the root of the external drive using the Advanced Security Settings dialog, then close the dialog box when it finishes. Next, reopen the Advanced Security Settings dialog and remove any "Unknown User" SID. With that completed; click the Add button, then in the "Select User or Group" dialog click Advanced, click "Find Now", then select your User Name and give yourself "Full Control" of "This folder, subfolders and files". When the permissions operation completes; close the dialogs and you'll have full control permissions to all the files on the external drive.

I did that. I actually did it another way and now the root folder in question has the "lock" icon on it, and I can still access it. However, the missing files and folders still aren't there. The OS literally doesn't see them. For example, it thinks my Videos folder is empty, when there's actually a few GB of files in it.

If you need data accessed from Windows, it would probably be best to put it on a NTFS partition. You could use FAT also, but I'm not a fan of that aside from removable drives. I don't even like it there, but the small size minimizes any data loss you might get.